Terahertz (THz) imaging is a compelling and competitive area of research for building next generation instruments. There are two methods researchers have developed for optical coupling to ultrasensitive devices at THz frequencies. The first method is absorber coupling to detectors, which can be realized for example with a thermometer that measures heat and temperature changes in an electromagnetic absorbing media in the signal band. However, it is difficult to find materials that absorb frequencies uniformly across the THz frequencies that are stable and absorb at high efficiency. The second method is to antenna couple to detectors. However, antenna coupling has inefficiencies similar to the first method (broadband bolometer) and in its simplest implementation can only detect a single color. However, it should be appreciated that at microwave and millimeter frequencies, a frequency diplexor can be used to detect multiple colors. But, at THz frequencies, the ohmic loss and required tolerances make direct implementation of this solution prohibitive from a practical perspective.
The high-resolution airborne wideband camera (HAWC) currently takes images in separate THz bands with a mechanical filter wheel, requiring temporal separation of the maps of different bands on a moving aircraft. For example, HAWC consists of a large format THz imager that selects one of its four frequency bands by rotating the filter wheel. The need to image each wavelength separately sets an upper limit to the mapping speed and spectral throughput of the instrument.
Furthermore, on a moving airplane, fast mapping speed is critical for obtaining good spectral data because of the Earth's changing atmospheric conditions during flight and the integration time available during the relatively short flight duration. The imager's large pixels do not allow, for example, Nyquist sampling of the sky with the stratospheric observatory for infrared astronomy (SOFIA) telescope, and the technology currently employed is unable to fill the entire SOFIA focal plane.